What is the difference between the microwave heating method and the traditional heating method

Microwave is a high-frequency electromagnetic waves, its frequency range of about 300 ~ 300 000MHz (the corresponding wavelength of 100 ~ 0.1cm) between 300MHz and 300GHz. It has volatility, high-frequency, thermal and non-thermal properties of the four basic characteristics. Microwave as a kind of electromagnetic wave also has wave-particle duality. Microwave quantum energy of 1 99 × l0 -25 ~ 1.99 × 10-22j. Its interaction with biological tissues is mainly manifested as thermal and non-thermal effects. Microwaves can be transmitted to the biological tissue so that the dipole molecules and proteins of the polar side chain to a very high frequency oscillation, caused by molecular electromagnetic oscillation and other effects, increasing the movement of molecules, resulting in the generation of heat. Microwaves are also capable of acting on hydrogen bonds, hydrophobic bonds, and van der Waals to redistribute them, thereby changing the conformation and activity of proteins. Non-thermal properties of living organisms a Biological effect is one of the important characteristics of microwaves, it has become an important aspect of medicine, cytology and other aspects of research, while it can also provide a theoretical basis for microwave physiotherapy or microwave surgery, etc. With the deepening of the understanding of the microwave heating technology, it has aroused the attention of many scientists, and in a number of aspects of the in-depth and extensive research.

1.1 microwave characteristics

1.1.1 selective heating

Substance absorption of microwave capacity, mainly by its dielectric loss factor to determine. Dielectric loss factor of large

Substance on the microwave absorption ability is strong, on the contrary, the dielectric loss factor of small substances to absorb microwave ability is

weak. Because of the differences in the loss factor of each substance, microwave heating shows the characteristics of selective heating.

Substances are different, the heat effect is also different. Water molecules are polar molecules, the dielectric constant is large, the medium

loss factor is also large, the microwave has a strong absorption capacity. Proteins, carbohydrates and other dielectric constant

number is relatively small, its microwave absorption capacity is much smaller than water. Therefore, for food, the amount of water content

has a great impact on the microwave heating effect.

1.1.2 Penetration

Microwaves are longer than other electromagnetic waves used for radiant heating, such as infrared, far-infrared and other wavelengths, because

this has a better penetration. Microwave penetration into the medium, due to medium loss caused by the increase in medium temperature,

so that the medium material inside, outside the almost simultaneous heating warming, the formation of the body heat source state, greatly reducing the conventional

heating in the heat conduction time, and in the conditions of the medium loss factor and the medium temperature is a negative correlation between the conditions of the medium,

the material inside and outside of the heating is uniform.

1.1.3 Thermal inertia

Microwave on the medium material is instantaneous heating temperature, energy consumption is also very low. On the other hand, the microwave output power

rate adjustable at any time, the medium temperature can be changed without inertia, there is no "residual heat" phenomenon, extremely conducive to

Automatic control and the need for continuous production.

1.2 microwave biological effect mechanism

When the microwave role in the organism, in the biological control system of the role and regulation, the organism is bound to establish a new equilibrium state in order to adapt to changes in the external electromagnetic environmental conditions, and therefore inevitably produces some biological effects. Microwave biological effects are mainly caused by the thermal effect of microwaves, followed by non-thermal effects.

1.2.1 microwave thermal effect

The microwave thermal effect on the organism refers to the microwave-induced biological tissues or systems heated and the physiological impact on the organism. Thermal effect is mainly polar molecules in the organism under the action of microwave high-frequency electric field repeatedly and rapidly oriented rotation and friction heat; ions in the body under the action of microwave vibration vibration energy will be converted into heat; general molecules will also absorb microwave energy to make the thermal movement energy increase. If the microwave energy absorbed by the organization of the organism is small, it can use its own thermal regulation system through the blood circulation will be absorbed microwave energy (heat) distributed to the whole body or outside the body. If the microwave power is very strong, the microwave energy absorbed by the biological tissue is more than the energy that can be distributed by the organism, then it will cause the body temperature of the site to rise. Elevated local tissue temperature will produce a series of physiological reactions, such as local vasodilatation, and through the thermal regulation system to accelerate blood circulation, tissue metabolism enhancement, leukocyte phagocytosis enhancement, to promote the absorption of pathological products and dissipation and so on.

1.2.1.1 Microwave heating advantages

The characteristics of microwave itself determines the microwave has the following advantages:

(1) rapid and uniform heating. No heat conduction process, and has an automatic thermal smooth performance to avoid overheating.

(2) high heating quality, less nutritional damage, can maximize the maintenance of food color, aroma, taste, reduce the destruction of vitamins in food.

(3) Safe and hygienic without pollution, strong sterilization of food. Because the microwave energy is controlled in the heating chamber made of metal and waveguide work, so the microwave leakage is effectively suppressed, no radiation hazards and harmful gas emissions, does not produce waste heat and dust pollution. Neither contaminated food, nor pollute the environment. Microwave sterilization in addition to the thermal effect has a biological effect, many germs in the microwave heating less than 100 ℃ when all killed.

(4) energy efficient. As the material containing water is very easy to absorb microwave heat directly, without other intermediate conversion links, so in addition to a small amount of transmission loss almost no other loss. It saves about 30%^-50% electricity than general conventional heating.

(5) has a rapid thawing function. In the microwave field, frozen food from the inside to the outside at the same time to absorb microwave energy, so that the frozen food as a whole heat, easy to form a whole uniform defrosting, shorten the defrosting time, and quickly over a 50C - 0 ℃ this easy to occur protein denaturation, food color change and flavor of the temperature band, in order to maintain the quality of the food does not deteriorate.

1.2.2 Microwave non-thermal effect

Microwave non-thermal effect is in addition to the thermal effect of other effects, such as electrical, magnetic and chemical effects. Under the action of microwave electromagnetic fields, some molecules in the organism will produce deformation and vibration, so that the cell membrane function is affected, so that the cell membrane inside and outside the liquid changes in the electrical status, resulting in a change in the role of biological changes, which can affect the central nervous system and so on. Microwave interference with bioelectricity (such as cardiac, cerebral, myoelectric, nerve conduction potential, cellular activity membrane potential, etc.) of the rhythm, will lead to cardiac activity, cerebral nerve activity and endocrine activity and a series of obstacles. The non-thermal effects of microwaves, people still do not know much. When the organism is irradiated by high power microwave, the thermal effect is the main (generally believe that the power density in the 10mW/cm2 more micro-thermal effect. And the higher the frequency of the thermal effect of the lower the threshold intensity); long-term low power density (1 m W / cm2 below) microwave radiation mainly caused by non-thermal effects.

1.3 microwave applications in agricultural science

Microwave germination of many low germination rate or slow germination of crops or forestry seeds have been germination test to explore whether it can improve the germination rate. Seed moisture content on the treatment effect has a significant impact, generally speaking, low moisture content of seeds by the heating treatment of the impact of large, but also can tolerate higher temperatures without damage. Microwave has a significant thermal effect, and has the effect of promoting G0 cells to enter the proliferation cycle (Carpita, N.C. & Murray W.N; 1976). In addition, Hu Yanyue et al. (1996) and Hu Xuanzhi et al. (1995), respectively, compared the biological effects of microwave and heat shock treatment of rice seeds, and at the same elevated temperature (45 ℃), the results showed that microwave treatment can be highly significant promotion of shoot vigor, and heat shock treatment can be highly significant promotion of root vigor . Lai Lin and Feng Hong (1997) utilized 50W, 200W and 500W microwave irradiation of Melaleuca alternifolia seeds, and found that 200W microwave treatment could significantly increase the germination rate, and at the same time could also significantly increase the germination conversation force. 200W microwave treated seeds were significantly higher than the control in amylase content from the 24th hour of germination onwards, and new enzyme bands of amylase isozymes were produced in the 48th period of the microwave treatment. This power of microwave can effectively stimulate the amylase enzyme in the germination period of Melaleuca alternifolia seeds, accelerate the metabolism of material and energy, and thus improve the vigor of seed germination. Huang Guiqin et al. (1999) used 105W microwave radiation of cucumber seeds for 10s and 20s, and found that early growth of true leaves. Plant height increased. The treatment of seeds for 30s, to promote early seedling emergence. However, with the prolongation of the growth period plant height was inhibited, the number of leaves also decreased. When the radiation dose of 105W, the time of treating seeds was 85, 10s, l4s, which promoted the growth of primary and lateral roots of cucumber seedlings and increased the activity of dehydrogenase, indicating that the root vigor was enhanced. Yang Junhong et al. (2003; 2004) studied the effect of microwave treatment on the germination characteristics of cabbage seeds and their salt tolerance using orthogonal tests. The results showed that: before microwave treatment, the salinity of the germination environment had the greatest effect on seed germination rate, and the effects of salinity and alkalinity were more significant; after microwave treatment, the effects of salinity and alkalinity of the germination environment on the seed germination rate were secondary and non-significant; the germination rate of the seeds under the preferred conditions was significantly higher than that of the control group. P. Reddy & D.J. Myeoek (2000) applied non-destructive and effective microwave irradiation of soybean seeds for 30 seconds promoted seed viability and activity but had no effect on cell and organelle structure.

1.4 microwave bioeffects in medicine

The use of microwave bioeffects can be used to diagnose a variety of tumors, chest diseases, emphysema, pulmonary edema, measuring the thickness of arterial blood vessel wall. In particular, the use of microwave bioeffects in the treatment of tumors has a special significance. Because the blood circulation and thermal conductivity of tumor tissues are poorer than that of normal tissues In the elbow of microwave irradiation, the temperature rise of tumor tissues is usually higher than that of the surrounding normal tissues by 1~3℃. If the heating temperature is properly controlled so that the temperature inside the tumor cells reaches 42 uc or more, the cancer cells can be killed without harming the healthy tissues. Therefore, the use of microwave can kill the radiation-resistant tumor cells that are lacking in oxygen and have low pH value. If microwave thermotherapy is combined with radiotherapy and chemotherapy, better therapeutic effect can be obtained. At present, experimental research work has been widely carried out, and many countries and regions are in the process of clinical application In recent years, thermotherapy has been carried out for liver cancer and cancerous lesions of brain tissues, and abundant information has been obtained (Chen Yi et al., 1999). Our scholars have achieved very obvious results in utilizing microwaves to treat liver cancer, rectal cancer and oral cancer. In addition, combining the scalpel blade with microwave radiation is also a form of application. Due to the microwave energy has the role of self-temperature and blood coagulation. And to a certain extent has the role of sterilization, so this form of scalpel is particularly suitable for fine blood vessels distributed very dense human tissue (Chen Yi et al., 1999). Examples include surgical procedures on the eyes and liver. What remains to be improved is how to make the energy of microwave radiation more concentrated. Thus, better results can be achieved. Similarly in the medical and pharmaceutical industries microwaves can be used for sterilization with fast and good results. In addition, with a strong pulse power to do wave irradiation of the brain of experimental animals. So that the temperature reaches 42 ℃ or more, can kill the animal in a few seconds. And make its brain enzyme system at the same time all uniform inactivation, thus suspending the biochemical reaction, so that the brain heat-resistant active substances can maintain the original composition, so that can be used to study the characteristics and function of neurochemistry.